Multi-cell saving

[kpinnipa]

Problem
Currently when multiple cells are saved, they are merged together into one code snippet and lose their individual cell structures. This means that when this snippet is inserted it is not possible to run each of the individual cells on their own.

Solution
Going forward, it would be better to save multi-cell snippets while maintaining their individual cell structures so that when the snippet is inserted, multiple cells will be available to run separately. Additionally, it would be good to allow for support of multiple cell types (code, markdown, etc).

Additional context
This would require changes to be made in the saving, editing, and the insertion process for multi-cell snippets.